Between is used when you refer to two people or things at one point of time. However when you refer to more than two people or things, you ought to use Among.

Let us keep this secret between three of us.

The statement might sound very familiar to you because it is often used by many. However the statement is incorrect for its use of ‘between’ as it is referring to three people. Hence the statement should go like this:

Let us keep this secret among three of us.

Here are a few more examples with correct usage of the two words:
* Keep the ball between your feet.
* Distribute the sweets among your classmates.
* There is a small passage between the two buildings.
* The rabbit disappeared among the bushes.